Hydraulic power generation, wind power generation and photovoltaic generation, which can improve environmental problems such as reduction of carbon dioxide and the like utilizing inexhaustible natural energy, are attracting attention. Among them, photovoltaic generation has been remarkably prevailing in recent years, because in addition to significant improvements in performances such as power generation efficiency of the solar cell module, reduction in cost have been progressed, and a project to facilitate introduction of a photovoltaic generation system for home use had been promoted by the government or municipalities. However, for further prevalence, further cost reduction is required, and therefore, a study aiming at further improvement in power generation efficiency has been continued night and day.
Solar cell module is generally the one in which a solar cell element such as silicon, gallium-arsenic, copper-indium-selenium and the like is protected with an upper transparent protective material and a lower substrate protective material, and the solar cell element and the protective material are fixed and packaged with an encapsulating material. Consequently, the encapsulating material for solar cell has been required to have a good transparency in order to obtain high power generation efficiency as well as superior adhesiveness to the protective materials and the solar cell element. Further, in order to avoid such troubles as flowing or deforming of the encapsulating material even when temperature rises during use of the solar cell module, it has been also required to have heat resistance. Further, in recent years, an encapsulating material more superior in flexibility has been required along with the thickness reduction of the solar cell element.
In addition, since semiconductor characteristics basically do not deteriorate although silicon cell is most expensive, there is a need to take out the silicon cell only from a module and reuse it when use of the module terminated or a malfunctioned member is exchanged in future. However, currently the encapsulating material has been cross-linked and cannot be removed even molten by heating. Further, it has become a problem that since a silane coupling agent has been added, strong adhesion between silicon cell and metal section makes difficult to separate them. Therefore, the encapsulating material is required to have a function to facilitate reuse of silicon cell
Currently, as an encapsulating material for solar cell element in a solar cell module, ethylene-vinyl acetate copolymer with a high content of vinyl acetate is used from the view point of flexibility and transparency. However, due to its insufficient heat resistance, adhesive property and the like, an organic peroxide or a silane coupling agent had to be used in combination. For this reason, two steps process had to be employed in which a sheet of ethylene-vinyl acetate copolymer compounded with these additives was prepared in advance, then a solar cell element is encapsulated using the resultant sheet. In the step to manufacture this sheet, since low temperature molding was required to avoid decomposition of the organic peroxide, extrusion molding rate could not be increased. Further, in the encapsulation step for a solar cell element, an adhesion process comprising a temporary adhesion step taking a time of several to several ten minutes on a laminator and a real adhesion step taking a time of several ten minutes to 1 hour at a high temperature allowing an organic peroxide to decompose in an oven had to be carried out. Therefore, manufacturing of the solar cell module cost time and labor, and the encapsulating material had been one of the factors to increase its manufacturing cost. In addition, such encapsulating material could not satisfy the request for reuse of the solar cell element as described above.    Patent Literature 1: JP-B-2-40709